The cost of communications grows in a quadratic fashion in
several directions as the number of replication nodes in a cluster
increases. Note the following relationships:

It is necessary to have sl_listen entries allowing connection from each node
to every other node. Most will normally not need to be very heavily,
but it still means that there needs to be n(n-1) paths.

Each SYNC applied needs to be reported back to all of
the other nodes participating in the set so that the nodes all know
that it is safe to purge sl_log_1 and sl_log_2 data, as
any "forwarding" node could potentially take over
as "master" at any time. One might expect SYNC messages
to need to travel through n/2 nodes to get propagated to their
destinations; this means that each SYNC is expected to get transmitted
n(n/2) times. Again, this points to a quadratic growth in
communications costs as the number of nodes
increases.

This points to it being a bad idea to have the large
communications network resulting from the number of nodes being large.
Up to a half dozen nodes seems pretty reasonable; every time the
number of nodes doubles, this can be expected to quadruple
communications overheads.